FIGS. 1 and 2 illustrate a portion of a conventional SOR generator disclosed, for example, in Japanese Unexamined Patent Publication No. SHO 62-276800. FIG. 1 shows a transverse cross-section of a portion of a vacuum pipe of the SOR generator where deflection magnets (not shown) are disposed, and FIG. 2 schematically shows a longitudinal cross-section of the portion of the vacuum pipe shown in FIG. 1.
In FIGS. 1 and 2, the reference numeral 1 denotes the vacuum pipe through which charged particles travel along an orbit 2. When charged particles which are traveling at a speed comparable with the speed of light are deflected, SOR 3 is generated in a direction tangent to the orbit 2 and impinges on the inner wall of the vacuum pipe 1 at a position 4. A bulk getter 5 is disposed at the SOR impinging position 4. The material for the bulk getter 5 may be, for example, zirconium or a zirconium alloy, such as Zr-Al and Zr-V-Fe.
In the conventional vacuum pipe of the above-described structure, the provision of the bulk getter 5 can suppress release of desorbed gas which would occur if the SOR 3 impinged directly on the structural material of the vacuum pipe 1. Impurities contained in the bulk getter 5 are ionized by the SOR 3 or by excited electrons generated by the SOR 3, and the thus produced ions diffuse inward of the bulk getter 5, whereby release of gas, desorbed in response to excitation by radiation, from the surface can be greatly suppressed. If the rate of ion diffusion into the bulk getter 5 is higher than the rate of generation in the bulk getter 5 of the ions due to excitation by radiation, the bulk getter 5 as a whole acts as an exhaust pump and, accordingly, can not only completely suppress the release of gas desorbed by radiation-excitation but also adsorb residual gas within the vacuum pipe 1.
In the above-described accelerator vacuum pipe 1, the bulk getter 5 is disposed only at the SOR radiation impinging position 4 and in its vicinity. This arrangement cannot provide adequate suppression of outgassing in other portions where the bulk getter 5 is not disposed, and, accordingly, the pressure within the vacuum pipe increases and the life of the stored charged-particles decreases.
The object of the present invention is to provide an accelerator vacuum pipe free of the above-described defects of the conventional vacuum pipe. According to the present invention, the vacuum pipe can be maintained at an ultra-high vacuum whereby a long storage life of charged particles can be obtained.